Since ultra-high molecular weight olefins, in particular, ultra-high molecular weight polyethylenes, have high molecular weights compared with general-purpose polyethylenes and thereby have excellent stretch processability, high strength, high chemical stability, and long period reliability, they have been used as starting materials of molded articles, such as microporous membranes for separators of secondary batteries represented by lead storage batteries and lithium ion batteries and fiber.
Ultra-high molecular weight olefins, in particular, ultra-high molecular weight polyethylenes, have various excellent characteristics, such as shock resistance, wear resistance, sliding property, low-temperature property, and chemical resistance, compared to general-purpose polyethylenes and have therefore been used in lining materials for, for example, hoppers and chutes; bearings; gears; roller guide rails; or molded articles, such as bone substitutes, bone conductive materials, and osteoinduction materials.
These ultra-high molecular weight polyethylenes have high molecular weights, and extrusion molding processing of such a resin alone is therefore difficult. Accordingly, in production of, for example, a microporous membrane for a secondary battery separator or fiber, an ultra-high molecular weight polyethylene powder is molded by kneading extrusion in many cases, for example, in an extruder in a state dissolved in a solvent under high temperature.
In addition, by the same reasons described above, molding by, for example, compression molding (press molding) and ram extrusion are also employed in many cases. It is important for both compression molded products and ram extruded products to achieve a balance between the shock resistance and the wear resistance. Examples of the method for achieving a balance between these characteristics are disclosed in Patent Literatures 1 to 3.